NBN ALN/NBN TUNNEL-JUNCTIONS FABRICATED AT AMBIENT SUBSTRATE-TEMPERATURE/

We have prepared NbN/AlN/NbN tunnel junctions at ambient substrate tem perature. The AlN barriers are fabricated by reactive rf magnetron spu ttering in the N-2 sputtering gas. We describe the electric and crysta lline properties of the MbN and AlN thin films, and discuss tunneling characteristics and the properties of the junction interface. Even tho ugh the NbN/AlN/NbN trilayers were deposited without intentional heati ng, the junctions had a large gap voltage (V-g = 5 mV), sharp quasipar ticle current rise (Delta V-g = 0.16 mV), and small subgap leakage cur rent (V-m = 25 mV). A high critical current density (J(c) = 8 KA/cm(2) ) is obtained in junctions with 1.5 nm thick AlN barriers. These resul ts show that high-quality NbN/AlN/NbN tunnel junctions can be prepared at ambient substrate temperatures.